1. Field of the Invention
The invention relates to a composite floor structure comprising a mortar layer set by a mineral agent and a the carrier plate substantially consisting of a flat basic element and a great number of upwardly projecting structural elements extending into the mortar, the elements having substantially the same height.
2. The Prior Art
Composite floor structures are adequately known and are employed, for example as subfloors when floor heating systems are to be installed. Such composite floor structures representing the subfloor for the final floor covering are based on the concept of the floating composition floor; i.e., the composition floor is separated from the supporting subfloor by a soft intermediate layer and is not connected with the latter but only rests on the intermediate layer. The composition floor is provided to serve as a load-distributing layer for uniformly admitting forces of load via the intermediate layer into the supporting subfloor, for example a concrete floor.
The carrier plate, which consists of an insulating material, is placed on the supporting subfloor. The upwardly projecting elements are uniformly distributed over the rectangular or square carrier plate. The heating tubes are maintained clamped between said elements, so that they do not change their positions when the paste-like composition floor is poured on. According to the concept of the floating composition floor, the thickness of the latter has to be dimensioned in such a way that the composition floor forms an inherently load-carrying floor plate. For assuring adequate load-carrying capacity it is recommended for this reason also in German ATV-DIN 18353 that the mortar covering above the projecting elements has a thickness of at least 45 mm. However, for floors subjected to higher loads it is recommended that the minimum thickness of the composition floor be increased. If cement composition floors are to be installed, it is necessary, furthermore, to reinforced such composition floors.
Based on the covering proposed by the above standard, the composition floors installed in the sector of residential construction work have a minimum overall thickness of 45 mm plus the diameter of the heating tubes. If such diameter comes to 18 mm, the total thickness of the composition floor amounts to 63 mm.
Mortars set with mineral agents, for example the composition floors addressed above, set with a certain loss of volume. The different water release properties and temperature influences acting on the top and bottom sides of the mortar layer lead to different changes in length when the mortar layer sets, with the result that the mortar bulges.
However, bulging of the mortar layer occurs particularly also if different moisture contents are contained in the installed mortar layer, for example when a higher content of moisture is present in the lower, deeper zone of the mortar layer than in the zone on top, which is close to the floor covering. This then leads to typical concave/convex deformation. If the mortar layer is covered with a rigid floor covering material, this leads to shear-off of the covering or to cracking.
Bulging of the mortar plate is unavoidable especially when floor heating tubes are installed. In the lower zone of the mortar layer adjoining the carrier plate, the temperature amounts to, for example about 40.degree. C. because of its direct contact with the heating tubes. However, as only a temperature of about 25.degree. C. is dissipated into the room on top of the floor covering, a temperature gradient of 15.degree. C. develops within the layer of mortar. When heating up, the lower regions of the mortar layer will therefore thermally expand to a distinctly higher degree than the upper zones of the mortar disposed close to the floor covering. With average room sizes of 18 to 20 square meters, bulging caused in this manner may be in the order of magnitude of up to 15 mm in height measured along the edges of the floor plate, with destruction of the marginal joint terminations in this process.
The effects bulging has on the floor are varied. For example, periodically recurring bulging, which naturally always develops in different locations in the mortar, for example in the course of the heating period in the winter and the nonheating period during the summer, may lead to growing denting of the carrier plate installed underneath the mortar layer, such plate consisting of insulating material, whereby such denting is caused by the pressure the plate applies due to the bulging of the structure of the mortar layer. Due to shifting of such pressure peaks the carrier plate disposed underneath the mortar is deformed to such an extent that the entire floor plate may sag in the course of some time.
The consequence of bulging of the layer of mortar is that certain areas of the latter lift off from the carrier plate or from its sublayers, so that even distribution of the forces in the carrier plate or in the sublayer is no longer possible. Under load, this then poses the risk that the mortar plate fractures for relieving the stress, forming a crack. Even though such fractures may go unnoticed with yielding floor coverings such as, for example, wall-to-wall carpeting, this will cause cracking also of rigid floor coverings installed on the mortar plate, for example such as tiles. Moreover, bulging leads to changes in the length of the top and bottom sides of the mortar layer. The shearing stress occurring as a result of such changes between the layer of mortar and the floor covering leads to detachment and even fracture of the rigid floor covering.
In order to counteract the phenomenon of bulging and the uncontrolled fracturing of the floor caused thereby, a change was made by reducing the degree of bulging by segmenting the floor areas, The individual mortar plates may then be separated from each other by expansion joints, trowel cuts, or so-called apparent or pseudo joints. Even though overall bulging of the individual mortar plates has been reduced in this manner, bulging still occurs to varying degrees within the individual segments, which may lead to unintended step-like bordering-up of individual floor segments against each other within the area of the joints. Furthermore, making provision for joints in the course of installation of the mortar is labor-intensive especially when larger floor areas--for example on sales premises or in larger residential rooms--have to be segmented with such expansion joints, which, moreover, need to be taken into account when the floor covering is installed later. Furthermore, mortar structures have to completely set first over at least 28 days according to acknowledged rules, so that shrinking is largely completed before a rigid floor covering can be applied. Even with composite mortar structures, whereby the mortar enters into a direct bond with the subfloor consisting of, for example concrete, the problem to be dealt with is that if the shrinking property of the subfloor is different from the one of the mortar, the layer of the latter becomes detached from the subfloor and cracking and bulging will then occur in the layer of mortar.